This invention relates generally to signal splitters that carry RF signals, DC power and low frequency AC control signals. This invention relates particularly to a signal splitter for connection to a coaxial cable that carries modulated video signals, DC power and low frequency control signals. Still more particularly, this invention relates to apparatus and methods for providing DC short circuit protection in a signal splitter for connection to a coaxial cable that carries RF video signals, DC power and low frequency control signals.
Many homes and businesses have video signal distribution systems for distributing video signals to two or more devices such as television receivers and video cassette recorders. The source of the video signal is typically an antenna or cable television (CATV) system. The video signals are typically distributed between various video devices via coaxial cables.
In a typical home where CATV is the video signal source, a decoder box is connected directly to the CATV outlet, and other devices receive video signals directly or indirectly from the decoder box. Signal splitters are typically used to interconnect the components of a video system. Television sets and video cassette recorders may often be operated by remote control systems for functions such as channel selection and volume control. Such control systems typically use infrared signals to transmit control signals between a hand-held transmitter and a receiver included in the video device. Ordinarily a direct line of sight is required between the transmitter and the receiver.
It is possible to use the coaxial cables that carry the video signals for carrying control signals and DC power. This permits a viewer in a location not having a direct line of sight between the receiver and the hand-held transmitter to have control of a decoder box, a VCR or a television set. The transmitter sends infrared (IR) control signals to an auxiliary receiver having a direct line of sight to the transmitter. The auxiliary receiver is connected to the coaxial video distribution cables and converts the IR control signals into electrical signals that are carried on the coaxial cables to a signal converter. The signal converter that converts the electrical signals back into IR control signals that are retransmitted via IR to the video device whose operation is to be controlled.
In modern video distribution systems it is possible to supply power to the signal converter by means of the coaxial cable. The signal converter may typically require 12 volts DC for its operation. Therefore, the coaxial cables carry video signals, control signals and DC power. A video system may include several components that draw DC power from the coaxial cable.
When all the components of a video system are properly connected, there is ordinarily no problem with using the coaxial cables to carry DC power and more than one type of AC signal. However, it is possible for components to be improperly connected during installation so that a DC short circuit exists. In present video systems a short circuit on one outlet of a signal splitter stops operation of the entire system and may damage the DC power supply. Determining the cause of the malfunction or locating an improperly connected device is similar to the problem of determining which light bulb is faulty in a series string of Christmas tree lights.